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Charge Limit feature suggestions

M

Mitchell Shnier

started a topic
over 2 years ago

I like to charge my Leaf to only 80% as this provides full regenerative braking (and may improve the lifetime of the battery). Also, I live in an area where electricity costs much less at night. So I would think it would be a very desirable OpenEVSE capability to be able to both charge only at night and only for a set amount of time or charge -- even if the car is left plugged-in for a few days.

I've tried using the OpenEVSE Charge Timer feature to only charge for a limited time (for example, from 4:00 am to 6:00 am, which adds 40% charge, so I only plug-in when the car is down to about 40% charge), and this works. Except if I don't drive the car the next day (and don't go to the garage to unplug it or send a $FD command to disable the charger), then it charges another two hours the next night, so charges to 100%. So the Charge Timer alone is not a solution.

I've tried using the Charge Limit feature and this doesn't work for a few reasons:

The feature seems to not work properly, as while it does terminate charging, after perhaps 10 to 25 minutes charging resumes. This might even be related to the Charge Limit set, as when I set it to 2 kW•h charging resumed after about ten minutes, and when I set it to charge 10 kW•h charging resumed after about 25 minutes. Is anyone else using this feature successfully. Perhaps it is because I also had a Charge Timer set.

Another problem is the Charge Limit is per-charge only, so I'd have to go through the button-pushes every time I charge. I think most people have a routine so it would be best if the selected Charge Limit was not a charge-session setting, but rather a selected option which remains set until cancelled.

Another problem is the Charge Limit gets cancelled if the Charge Timer is enabled. Perhaps there is some software reason to make these two features mutually exclusive, but it is the combination that would be needed in this case.

An alternative method to provide the capability needed would be to have an option that when the car finishes charging due to the Charge Timer feature, further charging (the next day) is disabled until the car is un-plugged and re-plugged.

On a related topic, if it simplifies the code (to make room for the above), I find it redundant to have both the Charge Limit and Time Limit feature, just one of those is all that is necessary. I'm loving my OpenEVSE, but it doesn't quite have what I think would be a very popular capability.

lincomatic

I think what you are really looking for is a function to charge to a specific SOC, which is not the intent of the Charge & Time Limit functions. Please join in on the discussion here:

https://groups.google.com/forum/#!category-topic/openevse/QJScKUq9vLI

It is really impossible to implement what you want, because the EVSE doesn't know anything about the SOC of your car. In order to do that, you would need to implement something via a device which can read SOC (such as a LeafCAN or other device that can read the SOC via the OBD-II port), and then use RAPI to terminate the charge when the required SOC is reached.

I am not sure why your car is resuming charge after 25 min when Charge Limit is set, and you are not having the same issue with Time Limit. Both methods terminate the charge using exactly the same mechanism. You can look at the code in J1772EvseController.cpp (search for "_LIMIT").

I have a 2013 Leaf, and both mechanisms don't cause it to restart the charge after it's terminated.

Also, once a limit is reached, the car will not resume charging no matter what the onboard timer wants to do.. when a limit is reached the EVSE goes into Sleep mode and stays there, so when my onboard timer fires, the car won't charge again. (This sometimes causes me trouble, because sometimes, I set a limit, override the timer to start charging, and don't use the car, leaving it plugged in overnight .. the limit is reached and the EVSE goes to sleep. Then when the onboard timer tries to top up the car overnight, the EVSE is still in Sleep mode, and no charging happens.. very unpleasant to wake up to an uncharged car!)

I'm a bit puzzled as to what's going on with your car. What year is it?

OpenEVSE Support

said
over 2 years ago

I am not sure it is impossible, the external device is the human brain. If you arrive with 3 bars in the leaf you have about 5kw so to get to 80% add 15kw. If you arrive with 6 bars add 10kw.

1 person likes this

M

Mitchell Shnier

said
over 2 years ago

Hello Lincomatic,

I'm happy to keep it simple and only plug in the car when it is down to, say, 40% charge, and have the OpenEVSE charge a fixed amount, such as another 40% (which for my 2016 Leaf's 30 kW•h battery would be 12 kW•h, by using the $SH 12 RAPI command).

I realize there are many more complicated things that could be done with customizing an Android App or using a Wi-Fi OBD-II dongle to automatically charge to a fixed State of Charge, but I just want something simpler and reliable, and am happy to only plug-in when I want 40% more charge.

I have not tried the Time Limit ($S3) feature, only the Charge Limit ($SH) -- neither of these would be enough on their own because I want to charge only at night when electricity is cheaper. I had used the Charge Timer ($ST) feature, and this almost did what I need (it both started charging only at night and limited charging to, for example, two hours). But the problem is then if I don't drive the car that day, it would charge another two hours the next night.

As you see from the attached files, the charging definately resumed after the Charge Limit feature had terminated it, perhaps 2016 Leafs briefly cycle drawing power after the EVSE terminates charging before 100% charge (maybe the Leaf is trying to "reset" the EVSE, as the Leaf would know it isn't fully charged). I did notice that when I plug the Leaf in outside of the Leaf's built-in Charging Timer schedule, the Leaf still charges for a few seconds, perhaps checking that the EVSE will provide power later when the Leaf's Charging Timer enables charging. Perhaps we need to see if other people with a 2016 Leaf also have their charge resume after using the OpenEVSE's Time Limit or Charge Limit feature.

lincomatic

Sorry, I didn['t read your original post closely enough. I didn't realize that you were talking about the EVSE's Timer rather than the Time Limit feature in conjunction with the Charge Limit.

I'm pretty sure that the reason the EVSE wakes up and resumes charging is because you also have the timer engaged. After the Charge Limit is reached, the EVSE goes to sleep. The problem is that the standby mode for the timer is also Sleep, so the timer can still engage once the limit is reached. I am really puzzled as to why it restarts after a 10-25 minute wait, though. The code actually checks the timer once per second.

One easy workaround that should do what you want is to use the timer in your Leaf instead of the one in the EVSE. Simply set your Leaf's timer to start it at the appropriate time. When you plug the car in, set the Charge Limit to your desired amount. When the Leaf's timer starts the charge, the EVSE will go to sleep after the Charge Limit is reached, and should stay in sleep until you unplug the car, even if you leave it plugged in for multiple days. If the Leaf tries to initiate a charge, the EVSE will ignore it, since it's in Sleep mode.

O

Oleksiy Yergiyev

said
about 1 month ago

Hi, sorry for bumping the thread. I found out as well that Charge Options won't provide for the set up of timer settings and energy limit concurrently, so that the charging session is stopped by any trigger event, whichever comes first. Is it still impossible to implement this in the firmware?

I was under impression that this option was available by checking https://openevse.openenergymonitor.org/ before buying the device, but now I have to resort to tweaking the timer settings and max current so that I get to the intended kWh during the session. Setting up an off-peak window AND energy limit would be a lot more convenient. It's possible to do this now, but in case the energy limit is completed first, the session continues (after restart?) anyway thus exceeding the target kWh amount.